The present invention relates to a reflecting mirror antenna unit, and is intended to provide a reflecting mirror antenna unit in which a radiation pattern due to the current distribution on the reflecting mirror can be varied readily.
With a conventional antenna unit of the type in which a radio wave radiated by a primary radiator thereof is reflected by a reflecting mirror, it is disadvantageous in that, even if the antenna unit is so designed that for instance a side lobe is low, the side lobe is higher than a desired one for instance because of errors involved in manufacturing the mirror surface. Among these side lobes, one formed in a direction near the bore-sighting axis is often due to the variation of the current distribution which is caused by deformation of the mirror surface. It is difficult to decrease this side lobe.
Heretofore, in order to decrease such a side lobe level, an antenna unit as shown in FIG. 1 is employed. In FIG. 1, reference characters 1a and 1b designate primary radiators, 2a and 2b directional couplers, 3 a resistance attenuator, 4 a phase unit and 5 a main reflecting mirror. The antenna unit is intended to eliminate the side lobe which is formed by an antenna system consisting of the main primary radiator 1a and the main reflecting mirror according to a method in which the primary radiator 1b is added and a part of the signals from the main feeding system, being branched to the directional couplers 2a and 2b, is fed to the primary radiator 1b with suitable phase and amplitude. That is, a particular side lobe can be eliminated by providing a beam which is equal in amplitude to and opposite in phase to the side lobe.
However, the method is disadvantageous in that, when it is required to eliminate a number of side lobes, the arrangement is necessarily intricate as much and accordingly is expensive.